基于量子点光放大器波长转换的啁啾特性研究

信号光的啁啾特性在很大程度上会影响量子点半导体光放大器(QD-SOA)的性能,引起传输信号的走离效应,使误比特率增高。为了改善这一特性,对QD-SOA全光波长转换器的啁啾特性进行了系统分析,基于QD-SOA的交叉增益调制效应的全光波长转换原理,采用牛顿法和4阶龙格-库塔法求解速率方程和光场传输方程,计算了注入电流、抽运光脉宽和抽运光消光比变化时QD-SOA全光波长转换器输出变换光的啁啾值。结果表明,增大抽运光脉宽、减小注入电流和抽运光消光比均可减小变换光的啁啾值,通过优化这些参量可以减小啁啾的影响,但在设计QD-SOA全光波长转换器时,要考虑抽运光消光比和变换光啁啾之间的均衡。     

Characterization of the chirp and intensity modulation propertiesof an SOA-MZI wavelength converter

Wavelength converters based on cross-phase modulation in semiconductor optical amplifiers (SOAs) in the arms of a Mach-Zehnder interferometer (MZI) provide a key network element for reconfigurable optical networks that incorporate wavelength routing. For system design purposes, the properties of the intensity and phase (chirp) modulation of the wavelength-converted signal for an SOA-MZI wavelength converter are important. In this paper, the small-signal α parameter, which characterizes the converter chirp, and the conversion frequency response are characterized experimentally for an integrated all-active SOA-MZI wavelength converter. For both co- and counterpropagating signals, the variation of the a parameter along the interference and conversion curves is considered in detail. Three optical modulators with quite different chirp properties are used to generate the modulated input signal to the wavelength converter. The results demonstrate that the chirp of the wavelength-converted signal is primarily determined by the device properties and the intensity of the modulated input signal. The a parameter of the wavelength-converted signal is negative for noninverting operation and positive for inverting operation. An important contribution of the paper is the detailed assessment of this key device characteristic. The experimental characterization of the wavelength converter is incorporated into a device model that can be used to obtain the pulse response. Calculated and measured results for the time dependence of the intensity and chirp of the wavelength-converted signal are in good agreement. The conversion frequency response for the intensity modulation is also measured along the conversion curve. The 3-dB bandwidth is found to be generally about 8-10 GHz     

Ultrawideband Wavelength Conversion Using Cascaded SOA-Based Wavelength Converters

An all-optical wavelength converter with a large wavelength hopping range is proposed and demonstrated. This converter consists of multistage cascaded wavelength converters using semiconductor optical amplifiers each with different gain band. Each of the cascaded wavelength converters enables us to perform both noninverted (NIV) and inverted (IV) operations. Conversion performance is compared at NIV and IV operations in terms of static characteristics as a function of input/output power of the converter. While good conversion performances are achieved at both operations, the IV wavelength conversion has better cascadability to obtain a high-quality converted signal for the cascaded scheme. Moreover, signal amplitude regeneration is demonstrated by repeating the IV wavelength conversion. Finally, we successfully demonstrate, for the first time, ultrawideband wavelength conversion, including over 300-nm wavelength hopping to the shorter wavelength side with a triple-stage cascaded wavelength converter     

增益调制型波长转换器消光比均衡的研究

利用半导体光放大器 (SOA)中交叉增益调制 (XGM)效应成功地实现了 62 2 Mb/ s和 2 .5Gb/ s信号的波长转换。对波长上 /下转换性能的研究表明 ,使用增益峰值波长比信号波长长的SOA可以有效地实现上 /下转换效率和消光比均衡 ,从而使这种类型的波长转换器在波分复用器(WDM)全光网中获得更大的应用     

Dimensioning of the Wavelength Converters in a WDM Optical Packet Switch

This paper analyzes the performances of a WDM optical packet switch making use of fiber delay lines to resolve output packet contentions; the optical packet switch is equipped with tunable wavelength converters which can shift optical packets to any wavelength of the output link which they are directed to. As not all packets need conversion, we propose a dimensioning technique allowing to reduce the number of converters and to improve the signal quality by reducing unnecessary conversions. The obtained results show that a remarkable reduction of the number of converters is obtained with respect to that needed by other switches described in literature. Such a saving is achieved by maintaining the packet loss probability below a prefixed threshold.     

利用NOLM同时实现两个波长的波长变换

最先利用非线性光学环路镜(NOLM)成功地将2.5Gbit/s的归零码光脉冲同时变换到不同的两个波长上.最大波长变换间距为35nm.实验系统中采用增益开关分布反馈半导体激光器(GS DFB-LD)产生的超短光脉冲作为控制光,采用分布反馈半导体激光器(DFB-LD)和波长可调激光器作为信号光.首次在1.55 μm波长段利用非线性光学环路镜进行波长变换过程时观测到了反相波长变换和脉冲畸变现象.     

利用半导体光放大器和滤波器组合实现高速波长转换和码型转换

将半导体光放大器(SOA)和滤波器组合使用是实现高速全光信号处理的有效途径。利用半导体光放大器和带宽为0.32nm的可调窄带滤波器同时实现了40Gbit/s的非归零(NRZ)信号的反相波长转换(WC)和非归零到伪归零(PRZ)信号的码型转换,波长转换和码型转换的结果差异取决于滤波器中心波长相对于探测光波长的失谐量。当滤波器的失谐量为-0.24nm时,输出反相的波长转换,此时滤波器起到加速半导体光放大器增益恢复的功能。当滤波器失谐量为 0.41nm和-0.48nm时,得到非归零到伪归零的码型转换,并且产生的伪归零脉冲分别出现在非归零信号的上升沿和下降沿,此时滤波器的作用是将探测光的相位信息转换为强度信息,并且该码型转换结果兼有波长转换的功能。     

Sparse Wavelength Conversion in Wavelength-Routed WDM Optical Networks*

A wavelength-routed optical network can suffer inefficiencies due to the wavelength-continuity constraint (under which a signal has to remain on the same wavelength from the source to the destination). In order to eliminate or reduce the effects of this constraint, a device called a wavelength converter may be utilized. Due to the high cost of these wavelength converters, many studies have attempted to determine the exact benefits of wavelength conversion. However, most of these studies have focused on optical networks that implement full wavelength conversion capabilities. An alternative to full wavelength conversion is to employ only a sparse number of wavelength converters throughout the network, thereby reducing network costs. This study will focus on different versions of sparse wavelength conversion--namely, sparse nodal conversion, sparse switch-output conversion, and sparse (or limited) range conversion--to determine if most of the benefits of full conversion can be obtained using only sparse conversion. Simulation and analytical results on these three different classes of sparse wavelength conversion will be presented. In addition, this study will present heuristic techniques for the placement of sparse conversion facilities within an optical network.     

Performance analysis of multi-fiber WDM network with limited-range wavelength conversion

Wavelength routed optical networks have emerged as a technology that can effectively utilize the enormous bandwidth of the optical fiber. Wavelength conversion technology and wavelength converters play an important role in enhancing fiber utilization and in reducing the overall call blocking probability of the network. In this paper, we develop a new analytical model to calculate the average blocking probability in multi-fiber link networks using limited-range wavelength conversion. Based on the results obtained, we conclude that the proposed analytical model is simple and yet can effectively analyze the impact of wavelength conversion ranges and number of fibers on network performance. Also a new heuristic approach for placement of wavelength converters to reduce blocking probabilities is explored. Finally, we analyze network performance with the proposed scheme. It can be observed from numerical simulations that limited-range converters placed at a few nodes can provide almost the same blocking probability as full range wavelength converters placed at all the nodes. We also show that being equipped with a multi-fiber per-link has the same effect as being equipped with the capability of limited-range wavelength conversion. So a multi-fiber per-link network using limited-range wavelength conversion has similar blocking performance as a full wavelength convertible network. Since a multi-fiber network using limited-range wavelength conversion could use fewer converters than a single-fiber network using limited range wavelength conversion and because wavelength converters are today more expensive than fiber equipment, a multi-fiber network in condition with limited-range wavelength conversion is less costly than a single-fiber network using only limited-range wavelength conversion. Thus, multi-fiber per-link network using limited-range wavelength conversion is currently a more practical method for all optical WDM networks. Simulation studies carried out on a 14-node NSFNET, a 10-node CERNET (China Education and Research Network), and a 9-node regular mesh network validate the analysis.     

利用SOA交叉增益调制实现2.5 Gbit/s非归零码的全光波长变换

采用半导体光放大器 (SOA)的交叉增益调制进行了 2 5Gbit/s的非归零码光脉冲的波长变换。向下波长变换间距大于 2 0nm ,向上波长变换间距大于 10nm。对变换信号测量了接收机入纤功率和误码率的关系。实验中采用同向变换的方式 ,信号光中心波长固定 ,探测光采用外腔半导体激光器 ,中心波长连续可调。对变换信号进行了至少 1h的测量 ,误码为零。为其在波分复用(WDM)网络中的应用奠定了基础。     

Performance Analysis of Multi-Fiber WDM Network with Limited-Range Wavelength Conversion

Wavelength routed optical networks have emerged as a technology that can effectively utilize the enormous bandwidth of the optical fiber. Wavelength conversion technology and wavelength converters play an important role in enhancing fiber utilization and in reducing the overall call blocking probability of the network. In this paper, we develop a new analytical model to calculate the average blocking probability in multi-fiber link networks using limited range wavelength conversion. Based on the results obtained, we conclude that the proposed analytical model is simple and yet can effectively analyze the impact of wavelength conversion ranges and number of fibers on network performance. Also a new heuristic approach for placement of wavelength converters to reduce blocking probabilities is explored. Finally, we analyze network performance with the proposed scheme. It can be observed from numerical simulations that limited range converters placed at a few nodes can provide almost the same blocking probability as full range wavelength converters placed at all the nodes. We also show that being equipped with a multi-fiber per-link has the same effect as being equipped with the capability of limited range wavelength conversion. So a multi-fiber per-link network using limited range wavelength conversion has similar blocking performance as a full wavelength convertible network. Since a multi-fiber network using limited range wavelength conversion could use fewer converters than a single-fiber network using limited range wavelength conversion and because wavelength converters are today more expensive than fiber equipment, a multi-fiber network in condition with limited range wavelength conversion is less costly than a single fiber network using only limited range wavelength conversion. Thus, multi-fiber per-link network using limited range wavelength conversion is currently a more practical method for all optical WDM networks. Simulation studies carried out on a 14-node NSFNET, a 10-node CERNET (China Education and Research Network), and a 9-node regular mesh network validate the analysis.     

All-optical wavelength conversion in optical multicarrier networks

The authors analyze the use of all optical wavelength conversion in the optical layer of a high-capacity transport network and compare different technological solutions. The analysis is based on the evaluation of the transmission performance of a generic signal path through the network. At least two technologies have been discovered allowing the realization of all-optical wavelength converters suitable for use in the considered application, providing high performance. In particular, for networks covering long distances, wavelength conversion based on four-wave-mixing in semiconductor amplifiers seems to be a very interesting solution     

Wide-range all-optical wavelength conversion usingdual-wavelength-pumped fiber Raman converter

A wavelength conversion scheme based on a fiber Raman converter is proposed, in which an externally injected high power pump laser and the associated Stokes laser are used to assist the Raman conversion process of signal light coded with optical information. Because the Raman gain spectrum in fibers is extremely broad, a wavelength conversion device with wide-range tunability is feasible. We numerically demonstrate that wavelength conversion from 1.31 to 1.42 μm can be realized using a fiber Raman converter at up to 10 Gb/s with an efficiency of 18%. It is also demonstrated that wide range conversion from 1.31 to 1.55 μm for optical fiber communication is feasible at up to 5 Gb/s when the fiber Raman converters are cascaded twice     

Wavelength Conversion in WDM Optical Networks: Strategies and Algorithms for Limiting the Number of Converters in the Optical Cross-Connects

This paper considers the problem of wavelength conversion in optical networks using wavelength division multiplexing technique. In the previous literature, two main wavelength routing and assignment strategies have been introduced: wavelength path (WP) and virtual wavelength path (VWP), depending on whether the signal stays on the same wavelength or is converted to another during its travel throughout the network. While the former method does not require any wavelength conversion, the latter needs wavelength conversion in each optical node and, in particular, a wavelength converter per each signal handled by the node itself. From the previous literature emerged that the VWP leads to optical cross-connect (OXC) with lower dimensions compared to the ones required by the WP scheme, and that the difference between the WP and VWP schemes increases as the number of wavelengths carried by each fiber increases. In this paper a new strategy is introduced, named partial virtual wavelength path (PVWP), with the related wavelength routing and assignment algorithm, which makes limited use of wavelength conversion compared to the VWP scheme, and allows the same advantages of VWP to be attained with lower OXC dimensions. The paper reports a comparative analysis among the different strategies, considering both the cases of a network without failures and a network with the possibility of failure restoration. The main result is that the proposed PVWP strategy allows the same advantages of the VWP scheme with a strongly reduced number of wavelength converters (around 5% of the number required by VWP scheme). This figure does not vary appreciably if failure restoration is considered. The new strategy can be adopted by using an opportune OXC architecture, as illustrated in the paper, which allow a limited number of converters to be shared among all the channels as a common pool.     

基于交叉增益调制的全光波长转换实验研究

分析了半导体光放大器交叉增益调制的基本原理,并利用该机制进行了2．5Gbit/s的非归零码光脉冲的波长转换。向上波长转换间隔大于14nm。最后,对转换信号测量了接收机入纤功率和误码率的关系曲线、光眼图、消光比和光信噪比等参数,结果发现转换信号眼图清晰,张开度大,消光比大于10dB,光信噪比大于30dB。实验表明采用半导体光放大器的交叉增益调制可以较理想地实现2．5Gbit/s的非归零码的全光波长转换。     

All-optical wavelength conversion: technologies and applications inDWDM networks

Dense WDM technologies make effective use of the vast fiber bandwidth and offer an added dimension to all-optical networks. Wavelength conversion at key network nodes is emerging as a fundamental functionality that can allow transparent interoperability, contention resolution, wavelength routing, and, in general, better utilization of the network resources under dynamic traffic patterns. We offer an overview of the enabling technologies and extend the treatment to the network application of these converters. Attention is given to semiconductor optical amplifiers and their use in wavelength converters. Converters based on four-wave mixing as well as those based on nonlinear optical loop mirrors are evaluated, paying special attention to signal integrity and architectural as well as performance issues. The use of wavelength converters in wavelength routing networks is explored together with the application of these devices in contention resolution and in the routing wavelength assignment problem. Future directions are outlined at the system as well as network levels     

Mirror-folded polarization-independent wavelength filter

A 1.55- mu m polarization-independent optical bandpass filter with a 3-dB bandwidth of 6 AA and a tuning range of at least 100 AA is demonstrated. The photonic circuit of the filter consists of a waveguide TE-TM mode splitter, two parallel electrooptic TE-to-TM, TM-to-TE mode converters as the wavelength selective element, and a reflective mirror at the far end of the crystal. The circuit can be viewed as a mirror-folded version of the polarization-independent filter. It is shown that by passing the light two times through the narrowband mode converters, the filter bandwidth can be reduced by about a factor of two compared to a conventional single-pass filter of the same length. A novel tunable mode converter structure is also demonstrated that allows coherent in-phase mode conversion during the two passes through the mirror-folded filter.<>     

Optimization of Optical Band-Pass Filters for All-Optical Wavelength Conversion Using Genetic Algorithms

We propose using genetic algorithms to numerically optimize optical band-pass filters (OBFs) for inverted and noninverted wavelength conversion based on semiconductor optical amplifiers. A fourth order Hermite-Gaussian sum series is used to describe the filter transfer function. Signal eye openings greater than 30 dB are obtained for both inverted and noninverted output signals. The dependence of the eye opening, overshoot and pulse amplitude fluctuation on variations in the filter center frequency and bandwidth is explored. We find that for an optimized eye opening in the noninverted signal the filter should be detuned towards lower frequency with respect to the probe frequency. Finally, we show that the optimum filter transfer function obtained with the genetic algorithm can be approximated with good agreement using an asymmetric Mach-Zehnder interferometer combined with a Gaussian OBF     

基于SOA的XPM波长转换器的噪声特性分析

研究了交叉相位调制(XPM)型波长转换器的噪声特性,讨论了如何选择XPM型波长转换器的注入电流等参量使系统处于最佳工作状态.结果表明:改变注入电流可使波长转换器周期性处于正相和反相工作状态,最佳的正反相工作点则位于使两臂半导体光放大器(SOA)的增益相等的注入电流附近.对于输入信号光和直流光功率,存在一个最佳功率值,使得波长转换的Q值最高.     

Characteristics of the Wavelength Converted Signal in Wavelength Conversion Based on Cross-Gain Modulation

An analytical theory describing the frequency chirp characteristics of the wavelength converted signal in wavelength conversion based on cross-gain modulation (XGM) in semiconductor optical amplifier (SOA) is derived. By computation, we can see that low input pump power, high probe power, small line-width enhancement factor and low unsaturated single-pass gain of the SOA are favorable for reducing the frequency chirp of the wavelength converted signal. The analytical results have significance in understanding and designing wavelength converters.